Film formation apparatus for semiconductor process and method for using the same

ABSTRACT

A method for using a film formation apparatus performs a first film formation process, while supplying a first film formation gas into a process field inside a process container, thereby forming a first thin film on a first target substrate inside the process field. After unloading the first target substrate from the process container, the method performs a cleaning process of an interior of the process container, while supplying a cleaning gas into the process field, and generating plasma of the cleaning gas by an exciting mechanism. Then, the method performs a second film formation process, while supplying a second film formation gas into the process field, thereby forming a second thin film on a target substrate inside the process field. The second film formation process is a plasma film formation process that generates plasma of the second film formation gas by the exciting mechanism.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a film formation apparatus for asemiconductor process for forming a film on a target substrate, such asa semiconductor wafer, and also to a method for using the apparatus. Theterm “semiconductor process” used herein includes various kinds ofprocesses which are performed to manufacture a semiconductor device or astructure having wiring layers, electrodes, and the like to be connectedto a semiconductor device, on a target substrate, such as asemiconductor wafer or a glass substrate used for an FPD (Flat PanelDisplay), e.g., an LCD (Liquid Crystal Display), by formingsemiconductor layers, insulating layers, and conductive layers inpredetermined patterns on the target substrate.

2. Description of the Related Art

In manufacturing semiconductor devices for constituting semiconductorintegrated circuits, a target substrate, such as a semiconductor wafer(made of, e.g., silicon) is subjected to various processes, such as filmformation, etching, oxidation, diffusion, reformation, annealing, andnatural oxide film removal. US 2003/0224618 A1 discloses a semiconductorprocessing method of this kind performed in a vertical heat-processingapparatus (of the so-called batch type). According to this method,semiconductor wafers are first transferred from a wafer cassette onto avertical wafer boat and supported thereon at intervals in the verticaldirection. The wafer cassette can store, e.g., 25 wafers, while thewafer boat can support 30 to 150 wafers. Then, the wafer boat is loadedinto a process container from below, and the process container isairtightly closed. Then, a predetermined heat process is performed,while the process conditions, such as process gas flow rates, processpressures, and process temperatures, are controlled.

In recent years, owing to the demands of increased miniaturization andintegration of semiconductor integrated circuits, it is required toalleviate the thermal history of semiconductor devices in manufacturingsteps, thereby improving the characteristics of the devices. Forvertical processing apparatuses, it is also required to improvesemiconductor processing methods in accordance with the demandsdescribed above. For example, there is a CVD (Chemical Vapor Deposition)method for a film formation process, which performs film formation whileintermittently supplying a source gas and so forth to repeatedly formlayers each having an atomic or molecular level thickness, one by one,or several by several (for example, Jpn. Pat. Appln. KOKAI PublicationsNo. 6-45256 and No. 11-87341). In general, this film formation method iscalled ALD (Atomic Layer Deposition) or MLD (Molecular LayerDeposition), which allows a predetermined process to be performedwithout exposing wafers to a very high temperature.

Further, WO 2004/066377 (Dec. 15, 2004), which corresponds to U.S. Pat.No. 7,094,708 B2, discloses a structure of a vertical processingapparatus for performing ALD, which utilizes plasma assistance tofurther decrease the process temperature. According to this apparatus,for example, where dichlorosilane (DCS) and NH₃ are used as a silanefamily gas and a nitriding gas, respectively, to form a silicon nitridefilm (SiN), the process is performed, as follows. Specifically, DCS andNH₃ gas are alternately and intermittently supplied into a processcontainer with purge periods interposed therebetween. When NH₃ gas issupplied, an RF (radio frequency) is applied to generate plasma so as topromote a nitridation reaction. More specifically, when DCS is suppliedinto the process container, a layer with a thickness of one molecule ormore of DCS is adsorbed onto the surface of wafers. The superfluous DCSis removed during the purge period. Then, NH₃ is supplied and plasma isgenerated, thereby performing low temperature nitridation to form asilicon nitride film. These sequential steps are repeated to complete afilm having a predetermined thickness. Apparatus of this type are alsodisclosed in Jpn. Pat. Appln. KOKAI Publications No. 2005-340787, No.2006-49808, and No. 2005-167027.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a film formationapparatus for a semiconductor process and a method for using the same,which can suppress a problem, such as particle contamination, found bythe present inventors, as described later, in broadening the applicationrange of a film formation apparatus utilizing plasma assistance.

According to a first aspect of the present invention, there is provideda method for using a film formation apparatus for a semiconductorprocess,

the apparatus comprising

a process container having a process field configured to accommodate atarget substrate,

a support member configured to support the target substrate inside theprocess field,

a heater configured to heat the target substrate inside the processfield,

an exciting mechanism including a plasma generation area inside a spacecommunicating with the process field,

a gas supply system configured to supply a process gas into the processfield, and

an exhaust system configured to exhaust gas from the process field, and

the method comprising:

performing a first film formation process, while supplying a first filmformation gas into the process field, thereby forming a first thin filmon a first target substrate inside the process field;

after unloading the first target substrate from the process container,performing a cleaning process of an interior of the process container,while supplying a cleaning gas into the process field, and generatingplasma of the cleaning gas by the exciting mechanism; and

then, performing a second film formation process, while supplying asecond film formation gas into the process field, thereby forming asecond thin film on a target substrate inside the process field, thesecond film formation process being a plasma film formation process thatcomprises generating plasma of the second film formation gas by theexciting mechanism.

According to a second aspect of the present invention, there is provideda film formation apparatus for a semiconductor process, the apparatuscomprising:

a process container having a process field configured to accommodate atarget substrate;

a support member configured to support the target substrate inside theprocess field;

a heater configured to heat the target substrate inside the processfield;

an exciting mechanism including a plasma generation area inside a spacecommunicating with the process field;

a gas supply system configured to supply a process gas into the processfield;

an exhaust system configured to exhaust gas from the process field; and

a control section configured to control an operation of the apparatus,

the control section executes

performing a first film formation process, while supplying a first filmformation gas into the process field, thereby forming a first thin filmon a first target substrate inside the process field;

after unloading the first target substrate from the process container,performing a cleaning process of an interior of the process container,while supplying a cleaning gas into the process field, and generatingplasma of the cleaning gas by the exciting mechanism; and

then, performing a second film formation process, while supplying asecond film formation gas into the process field, thereby forming asecond thin film on a target substrate inside the process field, thesecond film formation process being a plasma film formation process thatcomprises generating plasma of the second film formation gas by theexciting mechanism.

According to a third aspect of the present invention, there is provideda computer readable storage medium containing program instructions forexecution on a processor used for a film formation apparatus for asemiconductor process, the apparatus comprising a process containerhaving a process field configured to accommodate a target substrate, asupport member configured to support the target substrate inside theprocess field, a heater configured to heat the target substrate insidethe process field, an exciting mechanism including a plasma generationarea inside a space communicating with the process field, a gas supplysystem configured to supply a process gas into the process field, and anexhaust system configured to exhaust gas from the process field, whereinthe program instructions, when executed by the processor, cause the filmformation apparatus to execute:

performing a first film formation process, while supplying a first filmformation gas into the process field, thereby forming a first thin filmon a first target substrate inside the process field;

after unloading the first target substrate from the process container,performing a cleaning process of an interior of the process container,while supplying a cleaning gas into the process field, and generatingplasma of the cleaning gas by the exciting mechanism; and

then, performing a second film formation process, while supplying asecond film formation gas into the process field, thereby forming asecond thin film on a target substrate inside the process field, thesecond film formation process being a plasma film formation process thatcomprises generating plasma of the second film formation gas by theexciting mechanism.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a sectional view showing a vertical plasma film formationapparatus according to an embodiment of the present invention;

FIG. 2 is a sectional plan view showing part of the apparatus shown inFIG. 1;

FIG. 3 is a sectional plan view showing part of a modification of theapparatus shown in FIG. 1;

FIG. 4 is a flowchart showing the outline of a method for using theapparatus according to the embodiment of the present invention;

FIG. 5 is a timing chart showing gas supply and RF (radio frequency)application used in a cleaning process according to the embodiment ofthe present invention;

FIG. 6A is a graph showing a result concerning the number of particlesobtained by a comparative example in an experiment;

FIG. 6B is a graph showing a result concerning the number of particlesobtained by a present example in the experiment; and

FIG. 7 is a block diagram schematically showing the structure of a maincontrol section used in the apparatus shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

In the process of developing the present invention, the inventorsstudied problems to be caused in broadening the application range offilm formation apparatuses utilizing plasma assistance. As a result, theinventors have arrived at the findings given below.

Specifically, film formation apparatuses utilizing plasma assistanceincludes a mechanism for generating plasma and thus can be veryexpensive. It is therefore preferably for film formation apparatuses ofthis kind to be usable for performing a process using no plasma, such asa plasma-less film formation process. Where a plasma-less film formationprocess, such as a thermal CVD process or a thermal ALD or MLD process,is performed to form a film in a film formation apparatus of this kind,the RF power supply for plasma generation is set in the OFF-state.Further, wafers inside the process container are heated to and set at apredetermined temperature by a heater, and a necessary gas is suppliedinto the process container in this state.

However, when the plasma-less film formation process is performed,unnecessary by-product films are deposited on the inner walls of theprocess container and plasma chamber. The by-product films are partlypeeled off from the inner walls when a plasma film formation process isperformed after the plasma-less film formation process, due to theimpact of plasma generation and the sputtering action of plasma.Consequently, particles are generated and deposited on the wafers. Thisparticle generation is caused at a level of cumulative film thickness atwhich no particle generation is caused where the same film formationprocess is repeated. In general, plasma-less film formation processesentail a larger quantity of by-product films than that generated byplasma film formation processes.

Conventionally, there is a cleaning process for the interior of aprocess container by use of an etching gas of a halogen family, such asF family or Cl family, e.g., NF₃ gas or ClF₃ gas. However, where such acleaning process using a halogen family gas is performed, it takes timeto satisfactorily remove residual components of the F or Cl family fromthe process container. Further, a pre-coating process is required to setthe inner wall of the process container at a predetermined condition.Consequently, the cleaning operation takes a long time, therebydecreasing the operation rate of the film formation apparatus as awhole.

An embodiment of the present invention achieved on the basis of thefindings given above will now be described with reference to theaccompanying drawings. In the following description, the constituentelements having substantially the same function and arrangement aredenoted by the same reference numerals, and a repetitive descriptionwill be made only when necessary.

FIG. 1 is a sectional view showing a vertical plasma film formationapparatus according to an embodiment of the present invention. FIG. 2 isa sectional plan view showing part of the apparatus shown in FIG. 1. Thefilm formation apparatus 2 has a process field configured to beselectively supplied with a first process gas containing dichlorosilane(DCS) gas as a silane family gas, a second process gas containingammonia (NH₃) gas as a nitriding gas, and an assist gas comprising aninactive gas, such as N₂ gas. The film formation apparatus 2 isconfigured to form a silicon nitride film on target substrates by CVD inthe process field.

The apparatus 2 includes a process container (reaction chamber) 4 shapedas a cylindrical column with a ceiling and an opened bottom, in which aprocess field 5 is defined to accommodate and process a plurality ofsemiconductor wafers (target substrates) stacked at intervals. Theentirety of the process container 4 is made of, e.g., quartz. The top ofthe process container 4 is provided with a quartz ceiling plate 6 toairtightly seal the top. The bottom of the process container 4 isconnected through a seal member 10, such as an O-ring, to a cylindricalmanifold 8. The process container may be entirely formed of acylindrical quartz column without a manifold 8 separately formed.

The cylindrical manifold 8 is made of, e.g., stainless steel, andsupports the bottom of the process container 4. A wafer boat 12 made ofquartz is moved up and down through the bottom port of the manifold 8,so that the wafer boat 12 is loaded/unloaded into and from the processcontainer 4. A number of target substrates or semiconductor wafers W arestacked on a wafer boat 12. For example, in this embodiment, the waferboat 12 has struts 12A that can support, e.g., about 50 to 100 wafershaving a diameter of 300 mm at essentially regular intervals in thevertical direction.

The wafer boat 12 is placed on a table 16 through a heat-insulatingcylinder 14 made of quartz. The table 16 is supported by a rotary shaft20, which penetrates a lid 18 made of, e.g., stainless steel, and isused for opening/closing the bottom port of the manifold 8.

The portion of the lid 18 where the rotary shaft 20 penetrates isprovided with, e.g., a magnetic-fluid seal 22, so that the rotary shaft20 is rotatably supported in an airtightly sealed state. A seal member24, such as an O-ring, is interposed between the periphery of the lid 18and the bottom of the manifold 8, so that the interior of the processcontainer 4 can be kept sealed.

The rotary shaft 20 is attached at the distal end of an arm 26 supportedby an elevating mechanism 25, such as a boat elevator. The elevatingmechanism 25 moves the wafer boat 12 and lid 18 up and down in unison.The table 16 may be fixed to the lid 18, so that wafers W are processedwithout rotation of the wafer boat 12.

A gas supply section is connected to the side of the manifold 8 tosupply predetermined process gases to the process field 5 within theprocess container 4. Specifically, the gas supply section includes asecond process gas supply circuit 28, a first process gas supply circuit30, and an assist gas supply circuit 32. The first process gas supplycircuit 30 is arranged to supply a first process gas containing a silanefamily gas, such as DCS (dichlorosilane: SiH₂Cl₂) gas. The secondprocess gas supply circuit 28 is arranged to supply a second process gascontaining a nitriding gas, such as ammonia (NH₃) gas. The ammonia gasis also used as a cleaning gas for generating plasma during a cleaningprocess. The assist gas supply circuit 32 is arranged to supply aninactive gas, such as N₂ gas, as a purge gas or an assist gas foradjusting pressure. Each of the first and second process gases may bemixed with a suitable amount of carrier gas (such as N₂ gas), as needed.However, such a carrier gas will not be mentioned, hereinafter, for thesake of simplicity of explanation.

More specifically, the second process gas supply circuit 28, firstprocess gas supply circuit 30, and assist gas supply circuit 32 includegas distribution nozzles 34, 36, and 38, respectively, each of which isformed of a quartz pipe which penetrates the sidewall of the manifold 8from the outside and then turns and extends upward (see FIG. 2). The gasdistribution nozzles 34, 36, and 38 respectively have a plurality of gasspouting holes 34A, 36A, and 38A, each set being formed at predeterminedintervals in the longitudinal direction (the vertical direction) overall the wafers W on the wafer boat 12.

The nozzles 34, 36, and 38 are connected to gas sources 28S, 30S, and32S of NH₃ gas, DCS gas, and N₂ gas, respectively, through gas supplylines (gas passages) 42, 44, and 46, respectively. The gas supply lines42, 44, and 46 are provided with switching valves 42A, 44A, and 46A andflow rate controllers 42B, 44B, and 46B, such as mass flow controllers,respectively. With this arrangement, NH₃ gas, DCS gas, and N₂ gas can besupplied at controlled flow rates. The gas supply line 46 of the assistgas consisting of N₂ gas is connected to the gas supply line 42 of thesecond process gas through a line 47 provided with a switching valve47A. As needed, the switching valve 47A and so forth are controlled, sothat N₂ gas is spouted from the gas distribution nozzle 34.

A gas exciting section 50 is formed at the sidewall of the processcontainer 4 in the vertical direction. On the side of the processcontainer 4 opposite to the gas exciting section 50, a long and thinexhaust port 52 for vacuum-exhausting the inner atmosphere is formed bycutting the sidewall of the process container 4 in, e.g., the verticaldirection.

Specifically, the gas exciting section 50 has a vertically long and thinopening formed by cutting a predetermined width of the sidewall of theprocess container 4, in the vertical direction. The opening is closed bya partition plate 54 having a gas passage 55 and is covered with aquartz cover 56 airtightly connected to the outer surface of the processcontainer 4. The cover 56 has a vertically long and thin shape with aconcave cross-section, so that it projects outward from the processcontainer 4.

With this arrangement, the gas exciting section 50 is formed such thatit projects outward from the sidewall of the process container 4 and isconnected on the other side to the interior of the process container 4.In other words, the inner space of the gas exciting section 50communicates through the gas passage 55 of the partition plate 54 withthe process field 5 within the process container 4. The partition plate54 has a vertical length sufficient to cover all the wafers W on thewafer boat 12 in the vertical direction. The partition plate 54decreases the gas flow conductance between the gas exciting section 50and process field 5. Consequently, the pressure of the gas excitingsection 50 can be increased without adversely affecting the processfield 5 in terms of pressure.

A pair of long and thin electrodes 58 are disposed on the opposite outersurfaces of the cover 56, and face each other while extending in thelongitudinal direction (the vertical direction). The electrodes 58 areconnected to an RF (Radio Frequency) power supply 60 for plasmageneration, through feed lines 62. An RF voltage of, e.g., 13.56 MHz isapplied to the electrodes 58 to form an RF electric field for excitingplasma between the electrodes 58. The frequency of the RF voltage is notlimited to 13.56 MHz, and it may be set at another frequency, e.g., 400kHz.

The gas distribution nozzle 34 of the second process gas is bent outwardin the radial direction of the process container 4 and penetrates thepartition plate 54, at a position lower than the lowermost wafer W onthe wafer boat 12. Then, the gas distribution nozzle 34 verticallyextends at the deepest position (the farthest position from the centerof the process container 4) in the gas exciting section 50. As alsoshown in FIG. 2, the gas distribution nozzle 34 is separated outwardfrom an area sandwiched between the pair of electrodes 58 (a positionwhere the RF electric field is most intense), i.e., a plasma generationarea PS where the main plasma is actually generated. The second processgas-containing NH₃ gas is spouted from the gas spouting holes 34A of thegas distribution nozzle 34 toward the plasma generation area PS. Then,the second process gas is excited (decomposed or activated) in theplasma generation area PS, and is supplied in this state through the gaspassage 55 of the partition plate 54 onto the wafers W on the wafer boat12.

An insulating protection cover 64 made of, e.g., quartz is attached toand covers the outer surface of the cover 56. A cooling mechanism (notshown) is disposed in the insulating protection cover 64 and comprisescoolant passages respectively facing the electrodes 58. The coolantpassages are supplied with a coolant, such as cooled nitrogen gas, tocool the electrodes 58. The insulating protection cover 64 is coveredwith a shield (not shown) disposed on the outer surface to prevent RFleakage.

The gas distribution nozzles 36 and 38 of the first process gas andassist gas extend upward and face each other at positions near andoutside the partition plate 54 of the gas exciting section 50, i.e., onboth sides of the outside of the partition plate 54 (in the processcontainer 4). The first process gas containing DCS gas and the assistgas consisting of N₂ gas are spouted from the gas spouting holes 36A and38A of the gas distribution nozzles 36 and 38, respectively, toward thecenter of the process container 4. The gas spouting holes 36A and 38Aare formed at positions between the wafers W on the wafer boat 12 torespectively deliver the first process gas (containing DCS) and assistgas (N₂ gas) essentially uniformly in the horizontal direction, so as toform gas flows parallel with the wafers W.

On the other hand, the exhaust port 52, which is formed opposite the gasexciting section 50, is covered with an exhaust port cover member 66.The exhaust port cover member 66 is made of quartz with a U-shapecross-section, and attached by welding. The exhaust port cover member 66extends upward along the sidewall of the process container 4, and has agas outlet 68 at the top of the process container 4. The gas outlet 68is connected to a vacuum-exhaust system GE including a vacuum pump andso forth. The vacuum exhaust system GE has an exhaust passage 84connected to the gas outlet 68, on which a valve unit (an opening degreeadjustment valve) 86, a vacuum pump 88, and a detoxification unit 89 forremoving undesirable substances are disposed in this order from theupstream side.

The process container 4 is essentially airtightly surrounded by aheat-insulating casing 70. The casing 70 is provided with a heater 72 onthe inner surface for heating the atmosphere and wafers W inside theprocess container 4. For example, the heater 72 is formed of a carbonwire, which causes no contamination and has good characteristics forincreasing and decreasing the temperature. A thermocouple (not shown) isdisposed near the exhaust port 52 in the process container 4 to controlthe heater 72.

FIG. 3 is a sectional plan view showing part of a modification of theapparatus shown in FIG. 1. In this modification, the gas distributionnozzle 38 of the assist gas vertically extends at the deepest positionin the gas exciting section 50 along with the gas distribution nozzle 34of the second process gas, side by side.

The film formation apparatus 2 further includes a main control section48 formed of, e.g., a computer, to control the entire apparatus. Themain control section 48 can control the film formation process describedbelow in accordance with the process recipe of the film formationprocess concerning, e.g., the film thickness and composition of a filmto be formed, stored in the memory thereof in advance. In the memory,the relationship between the process gas flow rates and the thicknessand composition of the film is also stored as control data in advance.Accordingly, the main control section 48 can control the elevatingmechanism 25, gas supply circuits 28, 30, and 32, exhaust system GE(including the valve unit 86), gas exciting section 50, heater 72, andso forth, based on the stored process recipe and control data.

FIG. 7 is a block diagram schematically showing the structure of themain control section 48 of the apparatus shown in FIG. 1. The maincontrol section 48 includes a CPU 210, which is connected to a storagesection 212, an input section 214, and an output section 216. Thestorage section 212 stores process programs and process recipes. Theinput section 214 includes input devices, such as a keyboard, a pointingdevice, and a storage media drive, to interact with an operator. Theoutput section 216 outputs control signals for controlling components ofthe processing apparatus. FIG. 7 also shows a storage medium 218attached to the computer in a removable state.

The film formation method described below may be written as programinstructions for execution on a processor, into a computer readablestorage medium or media to be applied to a semiconductor processingapparatus. Alternately, program instructions of this kind may betransmitted by a communication medium or media and thereby applied to asemiconductor processing apparatus. Examples of the storage medium ormedia are a magnetic disk (flexible disk, hard disk (a representative ofwhich is a hard disk included in the storage section 212), etc.), anoptical disk (CD, DVD, etc.), a magneto-optical disk (MO, etc.), and asemiconductor memory. A computer for controlling the operation of thesemiconductor processing apparatus reads program instructions stored inthe storage medium or media, and executes them on a processor, therebyperforming a corresponding method, as described below.

Next, an explanation will be given of a method for using the filmformation apparatus 2 shown in FIG. 1. FIG. 4 is a flowchart showing theoutline of a method for using the apparatus according to the embodimentof the present invention.

The film formation apparatus 2 shown in FIG. 1 can be selectively usedto perform a plasma film formation process and a plasma-less filmformation process. For example, the plasma-less film formation processcorresponds to a thermal CVD process or a thermal ALD or MLD process.When a plasma-less film formation process is performed (Step S1 in FIG.4), by-product films are deposited on the inner walls of the processcontainer 4 and the cover 56 defining the gas exciting section 50.

Where the plasma-less film formation process is repeatedly performedcontinuously for a plurality batches, by-product films may be cleaned bya dry cleaning or wet cleaning process, as usual, when the cumulativefilm thickness of the film formation process exceeds a predeterminedvalue. However, when a plasma film formation process (Step S3 in FIG. 4)is performed after the plasma-less film formation process, even ifby-product films are thin, they are partly peeled off from the innerwalls (particularly the inner wall of the cover 56) due to the impact ofplasma generation and the sputtering action of plasma. Consequently,particles are generated and deposited on the wafers. For example, theplasma film formation process corresponds to a plasma CVD process or aplasma ALD or MLD process.

For this reason, as shown in FIG. 4, particularly when processes areswitched from the plasma-less film formation process (Step S1) to theplasma film formation process (Step S3), a plasma cleaning process (StepS2) is performed immediately before the plasma film formation process.This cleaning process is conceived to remove by-product films in advanceeven if they are thin, so that particles are note generated during theplasma film formation process of Step S3.

To be more precise, where an ordinary thermal CVD process is performedas the plasma-less film formation process (Step S1), operations areconducted as follows. Specifically, the wafer boat 12 at roomtemperature, which supports a number of, e.g., 50 to 100, wafers Whaving a diameter of 300 mm, is loaded into the process container 4heated at a predetermined temperature. Then, the interior of the processcontainer 4 is vacuum-exhausted and kept at a predetermined processpressure, and the wafer temperature is increased by the heater 72 to afilm formation process temperature of 650 to 800□, such as 750□. At thistime, the apparatus is in a waiting state until the temperature becomesstable. Then, the first process gas containing DCS gas and the secondprocess gas containing NH₃ gas are continuously supplied together fromthe respective gas distribution nozzles 36 and 34 at controlled flowrates. At this time, the wafer boat 32 is rotated along with the wafersW supported thereon. During the thermal CVD process, the RF power supply60 is set in the OFF-state, so that no plasma is generated.

The first process gas containing DCS gas is supplied from the gasspouting holes 36A of the gas distribution nozzle 36 to form gas flowsparallel with the wafers W. On the other hand, the second process gascontaining NH₃ gas is supplied from the gas spouting holes 34A of thegas distribution nozzle 34 through the gas passage 55 of the partitionplate 54 to form horizontal gas flows parallel with the wafers W. Whilebeing supplied between the wafers W, the DCS gas and NH₃ gas undergodecomposition and reaction by use of thermal energy applied from theheater 72. Consequently, a film formation material is provided, so thata silicon nitride film is formed on the wafers W. The gases thus usedare exhausted form the exhaust port 52 formed on the side opposite tothe partition plate 54.

Where a thermal ALD or MLD process is performed as the plasma-less filmformation process (Step S1), operations are conducted as follows.Specifically, the wafer boat 12 with wafers W supported thereon isloaded into the process container 4, as in the case described above.Then, the interior of the process container 4 is vacuum-exhausted andkept at a predetermined process pressure, and the wafer temperature isincreased by the heater 72 to a film formation process temperature of550 to 650□, such as 600□. At this time, the apparatus is in a waitingstate until the temperature becomes stable. Then, the first process gascontaining DCS gas and the second process gas containing NH₃ gas arealternately and intermittently supplied from the respective gasdistribution nozzles 36 and 34 at controlled flow rates. At this time,the wafer boat 32 is rotated along with the wafers W supported thereon.During the thermal ALD or MLD process, the RF power supply 60 is set inthe OFF-state, so that no plasma is generated.

The first process gas containing DCS gas is supplied from the gasspouting holes 36A of the gas distribution nozzle 36 to form gas flowsparallel with the wafers W. While being supplied, molecules of DCS gasand molecules and atoms of decomposition products generated by itsdecomposition (by use of thermal energy applied from the heater 72) areadsorbed on the wafers W. On the other hand, the second process gascontaining NH₃ gas is supplied from the gas spouting holes 34A of thegas distribution nozzle 34 through the gas passage 55 of the partitionplate 54 to form horizontal gas flows parallel with the wafers W. Whilebeing supplied, molecules of NH₃ gas and molecules and atoms ofdecomposition products generated by its decomposition. (by use ofthermal energy applied from the heater 72) react with molecules of DCSgas adsorbed on the surface of the wafers W, so that a silicon nitridefilm is formed on the wafers W.

Immediately after the step of supplying the first process gas containingDCS gas, and immediately after the step of supplying the second processgas containing NH₃ gas, the assist gas consisting of N₂ gas is suppliedas a purge gas into the process field 5. The assist gas is supplied fromthe gas spouting holes 38A of the gas distribution nozzle 38 to form gasflows parallel with the wafers W on the wafer boat 12. The assist gasflows thus formed serve to forcibly remove residual components withinthe process field 5, such as DCS gas and its decomposition products orNH₃ gas and its decomposition products. A cycle comprising these stepsis repeated a number of times, and thin films of silicon nitride formedby respective cycles are laminated, thereby arriving at a siliconnitride film having a target thickness.

After the plasma-less film formation process, the wafer boat 32 withwafer W supported thereon is unloaded. Thereafter, the cleaning process(Step S2) is performed, as described later in detail, and the plasmafilm formation process (Step S3) is then performed. The cleaning processmay be performed, after the wafer boat 12 used in the former process isset in an empty state with no wafers W supported thereon and is loadedinto the process container 4. Alternatively, the cleaning process may beperformed without, any wafer boat 12 loaded in the process container 4.

Where a plasma ALD or MLD process is performed as the plasma filmformation process (Step S3), operations are conducted as follows.Specifically, the wafer boat 12 with wafers W supported thereon isloaded into the process container 4, as in the case described above.Then, the interior of the process container 4 is vacuum-exhausted andkept at a predetermined process pressure, and the wafer temperature isincreased by the heater 72 to a film formation process temperature of300 to 650□, such as 600□. At this time, the apparatus is in a waitingstate until the temperature becomes stable. Then, the first process gascontaining DCS gas and the second process gas containing NH₃ gas arealternately and intermittently supplied from the respective gasdistribution nozzles 36 and 34 at controlled flow rates. At this time,the wafer boat 32 is rotated along with the wafers W supported thereon.

The first process gas containing DCS gas is supplied from the gasspouting holes 36A of the gas distribution nozzle 36 to form gas flowsparallel with the wafers W. While being supplied, molecules of DCS gasand molecules and atoms of decomposition products generated by itsdecomposition are adsorbed on the wafers W. On the other hand, thesecond process gas containing NH₃ gas is supplied from the gas spoutingholes 34A of the gas distribution nozzle 34 to form horizontal gas flowstoward the gas passage 55 of the partition plate 54. The second processgas is selectively excited and partly turned into plasma when it passesthrough the plasma generation area PS between the pair of electrodes 58.At this time, for example, radicals (activated species), such as N*,NH*, NH₂*, and NH₃*, are produced (the symbol ┌*┘ denotes that it is aradical). The radicals flow out from the gas passage 55 of the gasexciting section 50 toward the center of the process container 4, andare supplied into gaps between the wafers W in a laminar flow state. Theradicals react with molecules of DCS gas adsorbed on the surface of thewafers W, so that a silicon nitride film is formed on the wafers W.

Immediately after the step of supplying the first process gas containingDCS gas, and immediately after the step of supplying the second processgas containing NH₃ gas, the assist gas consisting of N₂ gas is suppliedas a purge gas into the process field 5. The assist gas is supplied fromthe gas spouting holes 38A of the gas distribution nozzle 38 to form gasflows parallel with the wafers W on the wafer boat 12. The assist gasflows thus formed serve to forcibly remove residual components withinthe process field 5, such as DCS gas and its decomposition products orNH₃ gas and its decomposition products. A cycle comprising these stepsis repeated a number of times, and thin films of silicon nitride formedby respective cycles are laminated, thereby arriving at a siliconnitride film having a target thickness.

Since the plasma ALD or MLD process utilizes plasma assistance to form asilicon nitride film, the film formation can be performed at a processtemperature lower than that of the thermal ALD or MLD process describedabove. When plasma of the second process gas containing NH₃ gas isgenerated, the electric power applied to the RF power supply 60 is setat, e.g., about 300 watts.

In place of the plasma ALD or MLD process, a plasma CVD process may beperformed as the plasma film formation process (Step S3). In this case,the first process gas containing DCS gas and the second process gascontaining NH₃ gas are continuously supplied together, while plasma iscontinuously generated to produce radicals of NH₃ gas. Also in thiscase, the electric power applied to the RF power supply 60 is set at,e.g., about 300 watts. In the plasma ALD or MLD process or plasma CVDprocess, the process temperature can be set to be lower than 650□, forexample.

Next, an explanation will be given of the cleaning process (Step S2).FIG. 5 is a timing chart showing gas supply and RF (radio frequency)application used in a cleaning process according to the embodiment ofthe present invention.

Where the cleaning process is performed, after the wafers W processed bythe plasma-less film formation process (Step S1) are unloaded, the waferboat 12 used in this former process is set in an empty state with nowafers W supported thereon and is loaded into the process container 4.Alternatively, the cleaning process may be performed without any emptywafer boat 12 loaded in the process container 4. In the latter case, theport of the process container 4 (i.e., the bottom port of the manifold8) is closed by a shutter disposed near the port in a well-known manner.

Then, the interior of the process container 4 is set at a predeterminedprocess pressure, and NH₃ gas used as a cleaning gas that can be excitedinto plasma is then intermittently supplied from the gas distributionnozzle 34 in a predetermined cycle (FIG. 5, (A)). In a period ofstopping NH₃ gas in this cycle (gap period), an inactive gas, such as N₂gas, is supplied from the gas distribution nozzle 34 (FIG. 5, (B)). TheN₂ gas thus supplied is used for promoting removal of peeled thin films.When N₂ gas is supplied from the nozzle 34, the switching valve 47A ofthe line 47 shown in FIG. 1 is set in an open state. At the same time,an inactive gas, such as N₂ gas, is continuously supplied from thedistribution nozzle 38 inside the process container 4 (FIG. 5, (C)).This N₂ gas is used for further promoting removal of peeled thin films.

Further, in synchronism with the supply timing of NH₃ gas, the RF powersupply 60 is controlled to turn on and off such that plasma is excitedat the time when the NH₃ gas is supplied (FIG. 5, (D)). Consequently,plasma is generated pulsewise, so that by-product films are efficientlypeeled off from the inner wall of the cover 56 due to a large impactforce of plasma ignition and the sputtering action of plasma.

The thin film thus peeled off are forcibly carried by the flow of N₂ gassupplied from the nozzles 34 and 38, and are exhausted through theexhaust port 52. At this time, it suffices if N₂ gas is supplied fromonly one of the two nozzles 34 and 38. As described above, plasma isgenerated while a cleaning gas that can be excited into plasma issupplied, so that by-product films deposited on the inner wall areremoved due to the sputtering action of plasma and so forth.Consequently, particle generation is satisfactorily suppressed in theplasma film formation process subsequently performed.

In the cleaning process, the pulse width T1 to turn on plasma is set tobe 1 second to 10 minutes, such as about 5 seconds. The period T2 of onecycle from the rising edge of a pulse of supplying NH₃ gas to the risingedge of the next pulse is set to be 1 second to 10 minutes, such asabout 25 seconds. The cleaning process is performed for, e.g., severalhours, depending on the cumulative film thickness. The flow rate of NH₃gas is set to be 0.1 to 10 liters/min, such as about 5 liters/min. Theflow rate of N₂ gas supplied from the nozzle 34 is set to be 0.1 to 10liters/min, such as about 3 liters/min. The flow rate of N₂ gas suppliedfrom the nozzle 38 is set to be 0.1 to 10 liters/min, such as about 3liters/min. The pressure inside the gas exciting section 50 is set forplasma to be generated, and is set to be not more than 10 Torr (1,333Pa), such as 0.5 Torr, where NH₃ gas is used, for example. Thetemperature inside the process container 4 is set to be 300 to 800□,such as about 650□.

The electric power applied to the RF power supply 60 to generate plasmain the cleaning process is set to be 100 to 1000%, and preferably 120 to500%, of the electric power applied to the RF power supply 60 togenerate plasma in the plasma film formation process subsequentlyperformed (Step S3). For example, the plasma electric power used in theplasma film formation process is set at, e.g., 300 watts, as describedabove, while the plasma electric power used in the cleaning process isset at, e.g., 350 watts. Consequently, almost all thin films that couldbe peeled off during the plasma film formation process are peeled offand removed by the cleaning process using an impact force provided by alarge electric power. Consequently, particle generation issatisfactorily suppressed in the plasma film formation process.

In other words, when plasma is generated during the plasma CVD process,the electric power used at this time is smaller than the electric powerused in the cleaning process. Unnecessary thin films that could bepeeled off by a smaller impact force provided by a smaller electricpower in the plasma CVD process have already been peeled off and removedby a larger impact force provided by a larger electric power in thecleaning process. Consequently, particle generation is satisfactorilysuppressed in the plasma CVD process.

In this embodiment, NH₃ gas used as a cleaning gas that can be excitedinto plasma is a gas to be used in the subsequent plasma film formationprocess. In this case, there is no risk of an undesirable impurity beingmixed into the film formed by the plasma film formation process.However, the cleaning gas may be any gas, as long as it includes nohalogen atoms, such as F atoms or Cl atoms, and can be excited intoplasma. For example, in place of NH₃ gas, an inactive gas, such as He,Ar, Ne, or Xe gas, may be used. Also in this case, there is no risk ofan undesirable impurity being mixed into the film formed by the plasmafilm formation process.

Accordingly, the cleaning process can be performed in a short time andimmediately followed by the subsequent plasma film formation process, sothat the operation rate of the apparatus is improved. In this respect,if a halogen family gas, such as F or Cl family gas, is used as acleaning gas, it takes time to satisfactorily remove residual componentsof the F or Cl family from the process container after the cleaningprocess. Further, a pre-coating process is required to set the innerwall of the process container at a predetermined condition, therebydecreasing the operation rate of the apparatus to a large extent.Accordingly, a halogen family gas is not suitable for this cleaning gas.

<Experiment>

Using the film formation apparatus shown in FIG. 1, an experiment wasconducted to confirm the relationship of the cleaning process relativeto the number of particles generated in the subsequent plasma filmformation process. In a comparative example, a series of processes wereperformed in the following order: a thermal CVD process (plasma-less)[cumulative film thickness: 0.65 μm]→a plasma ALD process→a plasma ALDprocess→a thermal CVD process (plasma-less) [cumulative film thickness:0.65 μm]→a plasma ALD process and a plasma ALD process. In a presentexample, a series of processes were performed in the following order: athermal CVD process (plasma-less) [cumulative film thickness: 0.65 μm]→acleaning process using plasma→a plasma ALD process→a plasma ALDprocess→and a plasma ALD process. After each of the processes, thenumber of particles of 0.18 μm or more deposited on the surface ofsamples of unloaded wafers W were counted while the surface wasirradiated with light. As sample wafers W, three wafers were selectedrespectively from the top (TOP), center (CTR), and bottom (BTM) of thewafer boat 12.

FIG. 6A is a graph showing a result concerning the number of particlesobtained by the comparative example in the experiment. FIG. 6B is agraph showing a result concerning the number of particles obtained bythe present example in the experiment. In FIGS. 6A and 6B, “T-CVD”denotes a thermal CVD process, and “P-ALD” denotes a plasma ALD process.

In the case of the comparative example shown in FIG. 6A, when the plasmaALD processes were performed after each of the thermal CVD processes, alarge number of particles were generated, such that the number ofparticles was 10,000 or more in each process. This was caused probablyby the fact that unnecessary films deposited on the inner wall of thegas exciting section 50 in each thermal CVD process were peeled off andchanged into particles by an impact force of plasma in each plasma ALDprocess

In the case of the present example shown in FIG. 6B, when the threeplasma ALD processes were continuously performed after the cleaningprocess, only a small number of particles were generated, such that thenumber of particles was about 50 at most in each process. Further, itwas confirmed that, during the plasma ALD process, the sputtering actionof plasma was always applied to the inner wall of the gas excitingsection 50, and thereby prevented unnecessary films from being depositedthereon.

In the embodiment described above, as shown in FIG. 5, (D), the cleaningprocess is arranged to excite plasma pulsewise in synchronism withintermittent supply of NH₃ gas. However, as shown in FIG. 5, (E), plasmamay be continuously generated, as a modification. In this case, since alarge impact force of plasma ignition is applied once, the effect ofpeeling off unnecessary thin films becomes lower than that obtained inthe case shown in FIG. 5, (D). However, even in this case, theunnecessary thin film can be sufficiently peeled off by the sputteringaction of plasma. Further, the pulsated gas supply of NH₃ gas shown inFIG. 5, (A), may be modified to continuously supply NH₃ gas, althoughthe gas consumption will be increased.

As shown in FIG. 3, where the gas distribution nozzle 38 is disposedinside the gas exciting section 50, N₂ gas may be continuously suppliedfrom the nozzle 38, as shown in FIG. 5, (C), so as to promote removal ofpeeled by-product films from the gas exciting section 50. In this case,supply of N₂ gas from the other nozzle 34 shown in FIG. 5, (B), may beunnecessary.

In the embodiment described above, as shown in FIG. 4, the cleaningprocess (Step S2) is performed when film formation processes areswitched from a plasma-less film formation process (Step S1), such as athermal CVD process or thermal ALD or MLD process, to a plasma filmformation process (Step S3), such as a plasma CVD process or plasma ALDor MLD process. However, regardless of plasma being used or not in afilm formation process, the cleaning process using plasma according tothe embodiment described above may be performed, when depositedby-product films reach a certain level. Consequently, it may be arrangedsuch that, after a film formation process using or not using plasma isperformed for certain lots of wafers, the cleaning process according tothe embodiment described above is performed, and then a film formationprocess using or not using plasma is performed.

In the embodiment described above, for example, the first process gascontains DCS gas as a silane family gas. In this respect, the silanefamily gas may be one or more gases selected from the group consistingof dichlorosilane (DCS), hexachlorodisilane (HCD), monosilane (SiH₄),disilane (Si₂Cl₆), hexamethyl-disilazane (HMDS), tetrachlorosilane(TCS), disilylamine (DSA), trisilylamine (TSA), andbistertialbutylaminosilane (BTBAS).

In the embodiment described above, the second process gas contains anitriding gas, which may be NH₃ gas or N₂ gas. Where the presentinvention is applied to formation of a silicon oxynitride film, anoxynitriding gas, such as dinitrogen oxide (N₂O) or nitrogen oxide (NO),may be used in place of the nitriding gas. Where the present inventionis applied to formation of a silicon oxide film, an oxidizing gas, suchas oxygen (O₂) or ozone (O₃), may be used in place of the nitriding gas.Further, a doping gas may be used for doping phosphorous or boron as animpurity. Further, in place of N₂ gas, another inactive gas, such as He,Ar, Ne, or Xe, may be used as an inactive gas for purging.

The present invention may be applied to a process for forming a filmother than a silicon nitride film, silicon oxynitride film, and siliconoxide film. The types of films formed before and after the plasmacleaning process may be the same or different. The target substrate maybe a substrate other than a semiconductor wafer, such as a glasssubstrate, LCD substrate, or ceramic substrate.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A method for using a film formation apparatus for a semiconductorprocess, the apparatus comprising: a process container having avertically elongated process field configured to accommodate a pluralityof target substrates, a support member configured to support the targetsubstrates at intervals in a vertical direction inside the processfield, a heater configured to heat the target substrates inside theprocess field, an exciting mechanism including a plasma generation areacommunicating with the process field and extending over a verticallength corresponding to the process field, with an electrode extendingalong the plasma generation area and configured to be supplied with anRF power for plasma generation, the plasma generation area being definedinside a cover attached on a sidewall of the process container with theelectrode extending along an outside of the cover, a process gas supplysystem configured to selectively supply a silicon source gas, an ammoniagas, and an inactive gas into the process field, such that the siliconsource gas is not supplied into the process field through the plasmageneration area and the ammonia gas is supplied into the process fieldthrough the plasma generation area, and the silicon source gas and theammonia gas are supplied to form essentially horizontal gas flows in theprocess field over a length corresponding to a vertical direction of theprocess field, and an exhaust system including an exhaust port disposedat a position facing the plasma generation area with the process fieldinterposed therebetween and configured to exhaust gas from the processfield, and the method comprising: performing a first CVD process, whilesupplying the silicon source gas and the ammonia gas into the processfield, thereby forming a first silicon nitride film on first targetsubstrates inside the process field, the first CVD process being athermal CVD process performed by heating the silicon source gas and theammonia gas by the heater without generating any plasma; unloading thefirst target substrates subjected to the first CVD process from theprocess container, and then performing a cleaning process of the plasmageneration area and the process field; and then, performing a second CVDprocess, while supplying the silicon source gas and the ammonia gas intothe process field, thereby forming a second silicon nitride film onsecond target substrates inside the process field, the second CVDprocess being a plasma CVD process performed by supplying the ammoniagas through the plasma generation area into the process field andgenerating plasma of the ammonia gas by the exciting mechanism whilesetting the RF power supplied to the electrode at a predetermined filmformation electrical energy, wherein the cleaning process comprises:intermittently supplying the ammonia gas pulsewise through the plasmageneration area into the process field and supplying a first part of theinactive gas through the plasma generation area into the process fieldcontinuously along with or pulsewise alternately with the ammonia gasintermittently supplied, while continuously supplying a second part ofthe inactive gas into the process field, not through the plasmageneration area, and while exhausting gas from the process field, andapplying the RF power to the electrode pulsewise to turn on the excitingmechanism in synchronism with the ammonia gas intermittently supplied tothereby cause plasma ignition impacts while the RF power is set at acleaning electrical energy, which is 120 to 500% of the film formationelectrical energy so as to intermittently generate plasma of the ammoniagas pulsewise a plurality of times, the impact of the plasma ignitionpeeling off by-product films deposited on an inner wall of the coverwhere the plasma generation area is located.
 2. The method according toclaim 1, wherein the cleaning process comprises alternately supplyingboth the ammonia gas and the first part of the inactive gas bothpulsewise.
 3. The method according to claim 1, wherein the cleaningprocess comprises continuously supplying the first part of the inactivegas while intermittently supplying the ammonia gas.
 4. The methodaccording to claim 1, wherein the cleaning process uses a cleaningtemperature of 300 to 800° C. set by the heater.
 5. The method accordingto claim 1, wherein the second CVD process uses a film formationtemperature of 300 to 650° C. set by the heater and comprisesalternately supplying the silicon source gas, and the ammonia gas andintermittently generating plasma of the ammonia gas pulsewise aplurality of times by the exciting mechanism.
 6. The method according toclaim 1, wherein the first CVD process uses a film formation temperatureof 650 to 800° C. set by the heater and comprises continuously supplyingthe silicon source gas and the ammonia gas at the same time.
 7. Themethod according to claim 1, wherein the first CVD process uses a filmformation temperature of 550 to 650° C. set by the heater and comprisesalternately supplying the silicon source gas and the ammonia gas.
 8. Themethod according to claim 1, wherein the support member is loaded intoand unloaded from the process container along with the targetsubstrates, and wherein the cleaning process is performed while thesupport member used for the first CVD process is set in an empty stateand placed in the process container.
 9. The method according to claim 1,wherein the silane source gas is selected from the group consisting of:dichlorosilane, hexachlorodisilane, monosilane, disilane,hexamethyldisilazane, tetrachlorosilane, disilylamine, trisilylamine andbistertialbutylaminosilane.
 10. The method according to claim 1, whereinthe inactive gas is selected from the group consisting of: N₂, He, Ar,Ne and Xe.
 11. The method according to claim 1, wherein the inactive gasis formed of N₂ gas.
 12. The method according to claim 1, wherein thecleaning process sets the plasma generation area at a pressure of notmore than 10 Torr (1,333 Pa).